Ensure using the given executable path. (dotnet/coreclr#10525)

Ensure using the given executable path. (dotnet/coreclr#10525)

* Ensure using the given executable path.

Fix the bug that corerun trying to load the executable from current directory even if the user has specified a full path of the executable.

Fix dotnet/coreclr#5631

* Revert "Ensure using the given executable path."

This reverts commit dotnet/coreclr@d237e6329f85132429176a0644cf6d93c9437ff4.

* Partially implemented.

* Ensure app context using correct IL file path.

Extracting simple name from the given file path and look up its value in tpa list. If the value does not equal to the given file path, we update the value with correct given file path.

Fix dotnet/coreclr#5631

* Re-arrange the slashIndex to eliminate unneccessary code.

* A few performance improvement with a memory leak bug fixed.

* Added the absolute path of target assembly to tpa list.

Fix dotnet/coreclr#5631

* Added the path of target assembly to tpa on Windows.

Fix dotnet/coreclr#5631

Commit migrated from https://github.com/dotnet/coreclr/commit/9e3ef8eb56d5027ed96348e89911afacbccee9f0